Sorry to be pedantic, but the word is etymology, without the "h". In Japanese it's 語源 or 日本語の語源. Any good website or book will be only in Japanese. If you're okay with that, you can try: http://gogen-allguide.com http://www.nihonjiten.com/gogen/nihongo/index.html Search Amazon JP for 日本語の語源 and you'll find a decent selection. There are also a couple of iOS apps (and probably some Android ones) although I haven't used them. I often use "Do you know the origins of ___?" when I'm with Japanese people. Great conversation always ensues and most Japanese will be scrambling to check their phones and Wikipedia to see if you're pulling their leg or not with your answer, and telling you you know more about Japan than Japanese people do.